The invention relates to a procedure for acoustically detecting microparticles, in particular for determining the appearance and/or positions of dispensed microparticles or for detecting the orientations of dispensers of a microparticle dispensing head, in particular for calibrating dispenser heads. The invention also relates to a procedure for executing such procedures, in particular to a detector for detecting the impact and/or impact position of microparticles released from a dispenser head.
It is generally known to place the smallest amounts of solid and/or liquid substances on a substrate with a microdispenser in the form of drops or solid particles (hereinafter generally referred to as microparticles). The microdispenser is used to apply defined volumes on the substrate at predetermined positions. A microdispenser can have a dispenser head with several dispensers, for example to position various substances on the substrate.
The microparticles released by a dispenser are generally so small that the function of a dispenser cannot be visually checked either qualitatively or quantitatively. However, malfunctions are extremely disadvantageous, since samples or reactants might inadvertently not be made to interact on substrates in the desired manner, for example during applications in biotechnology and genetic engineering. Therefore, there is interest in having a reliable measuring system with which the microparticles released by dispensers can be recorded.
There is also an interest in placing the samples or reactants on substrates with an extremely high surface density for the mentioned applications in biotechnology and genetic engineering. In addition to high accuracy and reproducibility for dispenser head positioning, this also requires knowledge of where the dispensed microparticles impact the substrate. Experience shows that the relative positions of the impact points do not correlate with the relative positions of the dispensers on the dispenser head. PCT/EP98/07559 describes this problem and various techniques for its resolution.
In earlier optical dispenser head calibrations performed with stroboscopic procedures, a new calibration principle was established by the technique underlying Patent Application PCT/EP98/07558. In this case, a dispenser head is repeatedly traversed over an optical or electroacoustic interaction area with linear borders while microparticles are released, and the impact of dispensed microparticles on the borders is detected. The impact times and geometric properties of the linear borders are used to determine the relative impact positions of the individual dispensers. This calibration technique offers the advantages of complete automation, high speed and reliability. However, the disadvantage to this technique is that the dispenser head must be repeatedly moved, or the accompanying system of coordinates must be activated repeatedly. In addition to the accuracy, this restricts primarily the speed of calibration.
There is interest in increasing the surface density of the samples applied to a substrate. This placed higher demands in particular on the accuracy of the dispensing head calibration.
The object of the invention is to indicate an improved procedure for microparticle detection, with which disposed microparticles can be recorded and/or localized at a higher rate and precision, and in particular which enables a functional check and/or calibration of dispenser head with an elevated accuracy and reproducibility. The object of the invention is also to indicate a detector for executing the mentioned procedure.
The invention is based on the idea of acoustically detecting the impact of a dispensed microparticle on a sensor target by having the microparticle impacting a sensor material (e.g., sensor film) of the sensor target trigger an acoustic wave that is detected with at least one sound converter. Depending on the application, the electric sound converter signal is evaluated only relative to the recording (detecting) of the microparticle or its localization.
In order to localize the microparticle, is it provided that the impact point (impact position) of at least one dispensed microparticle released by at least one dispenser be determined from the differences in run times required by an acoustic wave excited by the microparticles on the sensor material (e.g., stepped up sensor film) to pass from the impact position along at least three different predetermined paths to at least one oscillation or sound sensor (sound converter).
In a first embodiment of the invention aimed only at recording a dispensed microparticle, the acoustic wave is detected with at least one oscillation sensor connected with the sensor material, whose electrical sensor signal is evaluated for detecting the impact of the microparticle. To this end, the sensor signal is compared with a predetermined impact signal.
In a second embodiment of the invention also aimed at localizing a dispensed microparticle, the mentioned three paths are formed by a combination of at least two reflector elements and at least one oscillation sensor (or at least one reflector element and at least two oscillation sensors) on the sensor material (sensor film). The paths are the straight paths from the impact point directly to the oscillation sensor or from the impact point via the reflector elements to the oscillation sensor. In a third embodiment, at least three oscillation sensors are provided on the sensor material for particle localization. At least three straight paths are formed by the paths from the impact point directly to a respective oscillation sensor. The third embodiment is preferred due to a simplified setup and simplified signal evaluation.
The impact positions are determined from the run time differences as an absolute calculation, taking into account the known lengths of the paths and speeds of the acoustic waves, or as a relative determination by comparing the run time differences determined with various dispensers. In particular, the invention provides that the relative impact positions of dispensed microparticles from various dispensers of a dispenser head be determined by ascertaining reference run time differences for a reference dispenser of the dispenser head, and correlating the measured run time differences with the reference run time differences for all other dispensers of the dispensing head, and determining the relative impact positions from this.
The run time differences are preferably measured using a simple counting technique, for example by having one of the oscillation sensors where the surface wave is first detected emit a start signal to a counter, and having the remaining oscillation sensors emit a read signal to the counter on detection of the surface wave. The count differences each corresponding to the start and read signals are determined, and the run time differences are determined from this. The impact positions can be directly derived from the count differences. If a high-frequency counter module (counting rate in MHz range) is used as the counter, impact positions can be determined to within xcexcm accuracy.
Depending on the size of the oscillation target with the sensor material (sensor film or sensor film), the acoustic signals supplied following the impact of a microparticle can be determined for all dispensers of a dispenser head simultaneously, or for the individual dispensers in sequence (alternating with an adjustment movement of the dispenser head).
In particular, a detector according to the invention exhibits an oscillation target with a sensor material (especially with a clamped-on sensor film), with which reflector elements and at least one oscillation sensor are connected, depending on the embodiment. The oscillation sensors, which are preferably formed by capacitor microphones with oscillation couplers, or the reflector elements are spaced apart from each other.
According to a further preferred embodiment, the sensor foil is made from a piezoelectric material (piezoelectric foil). The oscillation sensors are formed by metallic layers which are deposited at predetermined positions on the foil. The metallic layers on the piezoelectric material fulfill the function of the above mentioned microphones.
The invention offers the following advantages. Microparticle detection according to the invention provides a direct monitoring and validation of dispenser function, e.g., during the manufacture of microdispensed substance grids. A robust, fast, highly precise and easily automatable dispenser head calibration is also enabled. The dispenser head to be calibrated does not have to be repeatedly moved over the oscillation target according to a specific path. It is enough to reproducibly set the dispenser as desired relative to the sensor film. While the dispensing procedure is in progress, the dispenser head must be moved. The relative positions of the impact points of dispensed microparticles can be determined with an accuracy of roughly 10 xcexcm (or under down to the 100 nm range). The acoustic particle detection takes place with a minimal evaluation time.